The invention relates to a shut-off flap for pressure spaces, in particular for vessels or pipelines, with a flap disc which is pivotable relative to an axis of rotation in a housing and which, in the sealing position, closes the throughflow through the housing in two mutually opposite flow directions in the region of a seal, the flap disc being arranged eccentrically, that is to say with an axis of rotation outside a seal center line, and the axis of rotation passing, in particular, through a major axis of the shut-off flap.
In pipelines carrying flowing media, the flow is interrupted by means of valves, slides or flaps. Flaps are preferred because of the markedly smaller overall length.
The simplest embodiment of a flap has an axis of rotation running centrally along the flap disc. An eccentric form of construction, in which the axis of rotation runs at a distance from the flap disc, is also known. This, as a rule, improves the sealing function of the flap disc, because the seal of the disc is not interrupted by the rotary shaft led out of the interior of the housing. Instead, said rotary shaft is seated in front of or behind the flap disc. Moreover, the axis of rotation or the rotary shaft is arranged centrally in front of the flap disc and intersects a major axis of the shut-off flap and therefore, as a rule, also the major axis of the pipeline.
Finally, what are known as double-eccentric flaps are known. In this type, in addition to the eccentricity described, the axis of rotation or the rotary shaft is arranged outside the major axis, that is to say at a short distance from the latter. This makes it possible to have a self-closing effect or positive closing for one flow direction. With regard to the other flow direction, there is the disadvantage of a permanent opening pressure, so that a likewise permanent and high closing force, with a correspondingly high drive torque, has to be applied. In the long term, particularly under relatively high line pressures, leakage points occur which make it impossible to work safely on the shut-off side of the pipeline.
Against this background, the object of the present invention is to provide a shut-off flap with an improved sealing action. Another object is to manage with lower drive torques.
In a development of the invention it is provided that the flap disc is self-closing in both flow directions. That is to say, the last portion of the closing movement is assisted by the resulting working pressure acting on the flap disc, irrespective of the flow direction. In the simplest instance, this is made possible by a centrally mounted flap disc which, in the closing position, has surfaces of different sizes laterally next to the axis of rotation in both flow directions, both the larger surfaces and the smaller surfaces in each case being located opposite one another diagonally with respect to the axis of rotation. This apparently impossible arrangement is made possible by a specific thickness of the flap disc and by a peripheral sealing surface which is sloped in lateral regions at the greatest distance from the axis of rotation. The seal then has laterally a three-dimensional depth in the direction of the major axis and in the direction of the diameter. It is precisely the depth in the direction of the diameter which makes it possible to provide different surface conditions for the two flow directions. That side of the flap disc which faces one flow is subdivided by the axis of rotation into a left and a right surface. The difference between the surfaces is relevant for generating the closing force. In a view of the flap disc according to the flow direction and with the flap disc closing clockwise, a positive closing effect is obtained when the left surface is larger than the right surface. The same condition is to be adhered to on the other side of the flap disc for the other flow direction. This is possible by means of the laterally obliquely directed sealing surface, so that what is referred to as the left flap surface on one side is larger than the right flap surface (opposite to it) on the other side.
Preferably, ring-like sealing elements are arranged, in particular, on the circumference of the flap disc and are pressed onto the peripheral sealing surface during the closing of the flap disc. In this case, a circumferential stress is built up, so that the pressure is distributed uniformly on the circumference and there is a high sealing action all-round.
The above-described slope of the sealing surface may be formed to a differing extent at the edges located laterally opposite one another or peripherally as a whole, so that what is referred to as a seat cone or taper is obtained. The flap disc may also be designed eccentrically, that is to say with an axis of rotation outside the flap disc or outside an associated seal center line. In this embodiment, too, in principle, positive closing in both flow directions is possible.
Advantageously, the axis of rotation is arranged on the major axis or intersects the latter. It thereby becomes simpler to design the shut-off flap. The forces and torques which occur are virtually symmetrical.
When the seat cone is used or arranged, a large seat-cone angle is advantageous for reducing the frictional forces during closing. The seat cone is defined by the position of the seat-cone axis or taper axis and by the position of the taper apex. The seat cone must be selected or calculated in such a way that it is impossible for the flap disc to be jammed in the sealing region. A particularly advantageous embodiment of the invention relates to a shut-off flap with a seat cone, the latter having a geometric shape determined according to specific criteria.
The position, peripheral sealing surface may, in other words, be reproduced as follows:
a. the peripheral sealing surface is part of a taper envelope, the generatrices of which define the angles of the sealing surface in relation to the major axis of the shut-off flap,
b. the generatrices intersect one another in the region of a taper apex, the position of which can be defined as follows:
b1. the seal center line intersects the major axis perpendicularly to the latter,
b2. the axis of rotation of the flap disc is arranged at a distance (eccentrically) from the seal center line, in particular on the major axis, and runs transversely to the seal center line and to the major axis,
b3. with the axis of rotation as the center point, a sealing circle is defined, the diameter of which is smaller than the nominal width of the pipeline or of the available inside diameter within the shut-off flap,
b4. intersection points of the sealing circle with the seal center line are designated as A and C, and the intersection point of the sealing circle with a straight line through A and with the center point is designated as B, B being located opposite the point A across the center point,
b5. a flap radius of half the distance from A to C is obtained,
b6. a line parallel to the major axis is at a distance from the latter corresponding to three times the flap radius, both the parallel line and the points B and C being located opposite the point A across the major axis,
b7. a tangent to the sealing circle through the point B intersects the line parallel to the major axis at a point which defines the taper apex.
It is expediently assumed, at the same time, that the taper apex and the center of rotation are located on different sides of the seal center line. The closing direction of the flap disc is also such that the latter, in its open position, is located opposite the taper apex across the major axis.
As stated in the first paragraphs of the description, eccentric or double-eccentric forms of construction are known. A shut-off flap having the features according to the invention makes it possible to design an eccentric form of construction in which the axis of rotation intersects, in particular, the major axis and actuation of the flap disc in both directions of rotation and in both flow directions is possible with substantially lower drive torques than in all the shut-off valves known hitherto. This also applies to designs in which a seal extending peripherally on the flap disc, for example a peripherally extending spring ring, is virtually as thin as desired in the flow direction. A flap disc of this type, admittedly, is no longer self-closing. Instead, a slight holding torque for maintaining the closed position of the flap disc may be necessary. However, the drive torque for opening the flap disc is likewise markedly lower than in the known shut-off flaps. The drive of the flap disc can have substantially smaller dimensions than hitherto. This is a great advantage precisely for quick-closing and opening flaps.
The use of a floating spring ring as a peripheral seal on the flap disc is another reason for the easy opening of the shut-off flap. This spring ring comes to rest, on the inside, on the conical seat of the peripheral sealing surface in the flap housing. The more the spring ring is pressed into the conical seat of the taper envelope, for example due to a pressure difference on the two sides of the flap disc or due to a drive torque, the higher a counterforce (force compensation) caused by the upsetting of the spring ring or a countertorque which is responsible for the easy opening of the flap disc becomes. The angles of the taper envelope are selected in such a way that there is freedom from jamming or there is no self-locking.
Finally, the invention also relates to different methods for the production of shut-off flaps. These relate, more specifically, to the machining of the sealing surfaces on the flap disc and on the housing. In practice, the seal consists of a peripheral sealing surface on the flap disc or on the housing and of corresponding sealing elements on the other part in each case. For example, a packing consisting of sealing rings or of lamellar seals may be provided. The sealing elements are machined in a similar way to the sealing surface. The flap disc is preferably provided with the sealing elements.
Further features of the invention, moreover, may be gathered from the claims and from the description.